The present invention relates generally to hearing systems, output transducers, methods, and kits. More particularly, the present invention is directed to hearing systems that comprise a plurality of activatable elements that are distributed on a support component to produce vibrations, that correspond to the ambient sound signals, on a portion of the human ear. The systems may be used to enhance the hearing process of those that have normal or impaired hearing.
Many attempts have been made to magnetically drive the eardrum and/or middle ear ossicles. To date, three types of approaches have been used. The first approach was to attach a permanent magnet, or a plurality of magnets, to one of the ossicles of the middle ear. A second approach was to attach super-paramagnetic particles to the outer surface of the ossicles using a collagen binder. The third approached suspended permanent magnets on the eardrum with a flexible support that clings to the eardrum through the use of a fluid and surface tension. The last approach is referred to herein as the “ear lens system,” and is described in commonly owned U.S. Pat. Nos. 5,259,032, 6,084,975 both to Perkins et al., the complete disclosures of which were previously incorporated herein by reference.
As shown in FIGS. 3A and 3B, in the conventional ear lens system, an output transducer assembly 26 comprises a magnetic frustum 28 that is embedded on a support component 14 that floats on a surface of the tympanic membrane 16. An input transducer (not shown) delivers a signal to the output transducer assembly 26 to cause a vibration in the tympanic membrane 16 that corresponds to the ambient sound received by the input transducer assembly.
While the ear lens system has been successful, the ear lens system can still be improved. For example, an alignment of the magnetic axis of the magnet with the applied magnetic field lines is important for the proper operation of the ear lens system. If the magnet is not properly aligned with the external field lines, it will not vibrate in a way that leads to the best transmission of sound into the ear. Thus, if the magnet is not properly aligned, the magnet may simply rotate rather than experience translational motion. Unfortunately, the alignment problem is made very difficult by the tortuous and irregularly shaped human ear canal anatomy. In addition, it varies greatly from person to person. Therefore, if one attempts to generate a magnetic field using a device located in the ear canal, it is often very difficult to align the generated magnetic field with the magnetic axis of the permanent magnet on the ear lens system. Moreover, the current needed to generate a magnetic field to drive the ear lens with both sufficient force to enable hearing assistance and still have the battery last a reasonable amount of time for a product is on the boundary of current battery technology capabilities. This leads to the need to precisely control the spacing of the transmitter generating the driving magnetic field and the ear lens magnet.
The inefficiency of magnets floating on the tympanic membrane was reported in seven subjects, by Perkins (1996). The average maximum gain of 25 dB was at 2 kHz. However, above 2 kHz the gain decreased and was more variable. The reduced gain at high frequencies is a primary cause for abandoning the previous approach.
Furthermore, it has been known that that the tympanic membrane has multiple modes of vibrations above 1-2 kHz (Tonndorf and Khanna 1970). It is now known that this results in motions of the umbo, at the center of the tympanic membrane, in the three dimensions of space (Decraemer et al. 1994). These modes of vibrations were not initially considered in the design of the electromagnetic systems described by Perkins et al. Part of the reason for the inefficiency has to do with rotational motion of the magnet (instead of translational movement) which is inefficiently coupled to the tympanic membrane.
Measurements by Decraemer et al. (1989) and subsequent model calculations (Fay 2001; Fay et al. 2002) suggest that at frequencies above 1-2 kHz, the motion of the tympanic membrane is significantly higher, by up to 20 dB, at the outer edge than at the center of the tympanic membrane. This suggests that an outer portion of the tympanic membrane can be actuated more efficiently. Several experiments showed that indeed a small magnet attached near the peripheral edge moved quite a bit. However, this motion is reduced by as much as 20 dB at the umbo and is thus not well coupled to the center of the drum due the higher impedance there. In addition, the umbo motion is smoothly varying and does not have the wild amplitude fluctuations present at the outer edge of the eardrum.
Consequently, what are needed are hearing systems, output transducers and methods that can actuate the center of the tympanic membrane and a periphery of the tympanic membrane differently, so as to better reflect the natural movement of the tympanic membrane.